Among hybrid vehicles, a plug-in hybrid vehicle uses a battery having a greater capacity than that of typical hybrid vehicles. When a driver drives for a short distance, the plug-in hybrid vehicle can operate in an electric vehicle (EV) mode only using a motor, thereby reducing the use of fossil fuel.
In addition, when the battery is exhausted while traveling for a long distance or through a crowded downtown area, the battery is charged by means of an engine or the vehicle can be propelled by the engine.
In order to maximize the performance of the plug-in hybrid vehicle, it is required to obtain optimum driving efficiency in both EV mode in which only the motor operates and engine mode in which only the engine operates.
The information disclosed in the Background is only for the enhancement of understanding of the background of the invention, and should not be taken as an acknowledgment or as any form of suggestion that this information forms a prior art that would already be known to a person skilled in the art.